1. Field of the Invention
The present invention involves a magnetic resonance imaging (MRI) technology. More particularly, it involves a method and a corresponding apparatus for reducing aliasing artifacts in the imaging for MR-monitored HIFU therapy.
2. Description of the Prior Art
In a magnetic resonance (MR) monitored high intensity focused ultrasound (HIFU) therapy system, the HIFU transducer, i.e. HIFU therapy head, emits a focused ultrasonic wave into the treated body through therapy water to increase the local temperature of the treated body part in a patient, thereby achieving the desired therapeutic result. FIG. 1 is a schematic diagram of an MR-monitored HIFU therapy system. As shown in FIG. 1, body 1 is lying on a bed 3, the primary coil 2 receives the MR signals from the body while the HIFU therapy head 5 is in the therapy water 4 and sends a focused ultrasonic wave to body 1 through the therapy water 4.
In practice, however, both the therapy head 5 for generating the ultrasonic waves and the therapy water 4 for conducting the ultrasonic wave to the body can also generate MR signals, which could add to the images to produce aliasing artifacts.
At present, several methods have been proposed for reducing the aliasing artifacts in MRI and one of these is to use an alternative liquid to replace water for conducting the ultrasonic wave to the body. However, water has so far proved to be the best liquid for transmitting ultrasonic signals and use of an alternative liquid will reduce the transmission rate of the ultrasonic wave, resulting in less satisfactory therapeutic results. Another proposal is to add a chemical agent to the water to prevent it from producing the MR signals; however such a chemical agent is often harmful to the human body, posing a greater risk to the patients. Currently, a more feasible method is to add a field of view (FOV) to include all water and therapy head in the imaging area, but this will inevitably increase the imaging time or reduce the image resolution of the area of interest (which is often a body part of the patients).